chore: housekeeping — linter & formatter setup

Add .prettierrc.json, .markdownlint.json, .yamllint.yaml, .gitattributes
Run CSharpier, Prettier and markdownlint across the entire codebase.
No logic changes — formatting, using order and line endings only.

.github/dependabot.yml

@@ -1,42 +1,42 @@
 version: 2
 
 updates:
-  # NuGet package updates for the plugin project. Weekly cadence keeps the
-  # noise down while still catching transitive security advisories within
-  # a few days of disclosure.
-  - package-ecosystem: nuget
-    directory: /HellionChat
-    schedule:
-      interval: weekly
-      day: monday
-      time: "07:00"
-      timezone: Europe/Berlin
-    open-pull-requests-limit: 5
-    labels:
-      - dependencies
-      - nuget
-    commit-message:
-      prefix: "chore(deps)"
-    groups:
-      patches:
-        update-types:
-          - patch
-      minor:
-        update-types:
-          - minor
+    # NuGet package updates for the plugin project. Weekly cadence keeps the
+    # noise down while still catching transitive security advisories within
+    # a few days of disclosure.
+    - package-ecosystem: nuget
+      directory: /HellionChat
+      schedule:
+          interval: weekly
+          day: monday
+          time: "07:00"
+          timezone: Europe/Berlin
+      open-pull-requests-limit: 5
+      labels:
+          - dependencies
+          - nuget
+      commit-message:
+          prefix: "chore(deps)"
+      groups:
+          patches:
+              update-types:
+                  - patch
+          minor:
+              update-types:
+                  - minor
 
-  # GitHub Actions versions in .github/workflows. Lower cadence because
-  # Action releases ship less frequently and are usually safe to defer
-  # for a month.
-  - package-ecosystem: github-actions
-    directory: /
-    schedule:
-      interval: monthly
-      time: "07:00"
-      timezone: Europe/Berlin
-    open-pull-requests-limit: 3
-    labels:
-      - dependencies
-      - github-actions
-    commit-message:
-      prefix: "chore(actions)"
+    # GitHub Actions versions in .github/workflows. Lower cadence because
+    # Action releases ship less frequently and are usually safe to defer
+    # for a month.
+    - package-ecosystem: github-actions
+      directory: /
+      schedule:
+          interval: monthly
+          time: "07:00"
+          timezone: Europe/Berlin
+      open-pull-requests-limit: 3
+      labels:
+          - dependencies
+          - github-actions
+      commit-message:
+          prefix: "chore(actions)"